The Neogene strata of offshore eastern Canada contain a rich diversity of dinoflagellate cysts. Among the most distinctive are species of the peridinialean genus Sumatradinium and the related genera Barssidinium gen.nov. and Erymnodinium gen.nov. Sumatradinium and Erymnodinium have a reticulate wall, whereas Barssidinium has a smooth to granulate wall. Sumatradinium and Barssidinium have processes or pustules only; Erymnodinium has crests. The three genera and their constituent species are useful for biostratigraphic subdivision in the Miocene and Pliocene, as exemplified in the two wells Evangeline H-98 and Heron H-73; stratigraphic control for these wells is based on previously established palynologic data. To categorize the considerable morphological variation of these genera and promote their biostratigraphic usefulness, we propose five new species: Sumatradinium druggii, Sumatradinium pustulosum, Barssidinium evangelineae, Barssidinium graminosum, and Barssidinium wrennii. We also emend the generic diagnosis of Sumatradinium and the specific diagnosis of Sumatradinium hispidum.